There are many factors and constraints that influence designs of lock and trim assemblies, including whether a clutch mechanism or a stop mechanism is employed to lock the door, the number of lock functions supported, the strength of the lock, the ability of the lock to thwart an attack, and the cost of manufacture. Each design constraint compounds the complexity of such a design, because attempting to accommodate a given design constraint may restrict one's ability to accommodate a different design constraint. Because not all designs are equally effective or practical, and because changing circumstances continually give rise to new design constraints, there is always a need for innovation.
For example, when choosing a replacement trim assembly for a door, it is important to find a trim assembly that is compatible with the spindle and possibly other elements of the interior latching assembly, that matches the door function (e.g., is it an interior door or an exit door), that is compatible with the handedness of the door, that matches the physical dimensions and relative placement of the mortise and/or bore cylinder, and that matches the physical arrangement of trim mounting holes.
Most trim assemblies, however, are only suitable for a specific type or make of lock. It would be advantageous to have a universal trim assembly that, with minimal substitution or rearrangement of parts, accommodates a wide variety of types and makes of locks, as well as a wide variety of lock functions. However, the design of such an assembly is complicated by the typically tight spacing of trim assembly components. For example, a rearrangement of the trim mounting posts may require a rearrangement of other trim assembly components.
As another example, it is desirable to design a lock in a manner that thwarts attempts to defeat it. One common method of attack is to apply a crowbar or long wrench to the door handle or lever. Another method of attack is to apply a powerful blow to the door or trim assembly. Yet another method of attack is to manipulate internal steel components of the lock using a strong magnet.
As yet another example, many lock mechanisms require a door handle to be in a neutral, non-latch-retracting position in order to lock the handle. It is therefore advantageous for the trim assembly to incorporate a return spring to bias the handle back to the neutral position and an escapement spring to engage the lock when the handle returns to the neutral position.
U.S. Patent Publication No. 2001/0005998 A1 describes a clutch mechanism for an electronic lock in which a motor drives an endless screw which in turn drives a spring connected to a lever of a yoke that engages and disengages a clutch element. The clutch mechanism may be susceptible to tampering. For example, an impact might cause the clutch to become engaged, allowing an intruder to break in.
Improved clutch-type trim assemblies are needed that can be applied to a greater number of pre-existing existing latch assemblies, that support latch retraction through lever rotation in either direction from a neutral position, and that are better able to thwart an attack.
The present invention described below can be characterized in many different ways, not all of which are limited by its capacity to address the above-mentioned issues, needs or design constraints.